A variety of oxygen-carrying complexes of cobalt, derivatives of Co Salen, will be synthesized and crystallized as their dioxygen adducts. In addition we will make similar complexes, with iron, manganese, chromium, vanadium, copper, etc., as central metal atoms. These will be screened for oxygen-carrying activity. By varying the substituents on the chelate, the added base, the metal, the solvent, and the temperature of crystallization, we hope to be able to form crystals suitable for X-ray structural determinations. We have synthesized approximately 30 cobalt complexes already; these will be used in a program to find optimum conditions of solvent, axial base, and crystallization temperature for the dioxygen adducts.